Zarr v3: support root path (#1085)

* support path='/' for zarr v3 to create a root array or group

v3 spec states path = '/' for arrays gives /meta/root.array.json
               path = '/' for groups gives /meta/root.array.json

In this implementation path = None or path = '' will also result in
a root array. Creation routines default to path=None, so this makes
it so that the path argument does not have to be manually specified.

* revert change to normalize_storage_path

update additional tests

* fix

* update TestArrayV3 to inherit all tests from TestArray

* remove test bypass

* fix nbytes_stored for v3 array without path

update test_nbytes_stored to handle both v3 and v2 cases properly

* pep8

* fix incorrect default value for at_root in _init_creation_kwargs

previous behavior corresponded to at_root=True by default

* flake8

zarr/_storage/store.py

@@ -420,23 +420,23 @@ def _listdir_from_keys(store: BaseStore, path: Optional[str] = None) -> List[str
 
 def _prefix_to_array_key(store: StoreLike, prefix: str) -> str:
     if getattr(store, "_store_version", 2) == 3:
+        sfx = _get_metadata_suffix(store)  # type: ignore
         if prefix:
-            sfx = _get_metadata_suffix(store)  # type: ignore
             key = meta_root + prefix.rstrip("/") + ".array" + sfx
         else:
-            raise ValueError("prefix must be supplied to get a v3 array key")
+            key = meta_root[:-1] + '.array' + sfx
     else:
         key = prefix + array_meta_key
     return key
 
 
 def _prefix_to_group_key(store: StoreLike, prefix: str) -> str:
     if getattr(store, "_store_version", 2) == 3:
+        sfx = _get_metadata_suffix(store)  # type: ignore
         if prefix:
-            sfx = _get_metadata_suffix(store)  # type: ignore
             key = meta_root + prefix.rstrip('/') + ".group" + sfx
         else:
-            raise ValueError("prefix must be supplied to get a v3 group key")
+            key = meta_root[:-1] + '.group' + sfx
     else:
         key = prefix + group_meta_key
     return key
@@ -449,7 +449,7 @@ def _prefix_to_attrs_key(store: StoreLike, prefix: str) -> str:
         if prefix:
             key = meta_root + prefix.rstrip('/') + ".array" + sfx
         else:
-            raise ValueError("prefix must be supplied to get a v3 array key")
+            key = meta_root[:-1] + '.array' + sfx
     else:
         key = prefix + attrs_key
     return key

zarr/creation.py

@@ -163,7 +163,7 @@ def create(shape, chunks=True, dtype=None, compressor='default',
     dimension_separator = normalize_dimension_separator(dimension_separator)
 
     if zarr_version > 2 and path is None:
-        raise ValueError("path must be supplied to initialize a zarr v3 array")
+        path = '/'
 
     # initialize array metadata
     init_array(store, shape=shape, chunks=chunks, dtype=dtype, compressor=compressor,

zarr/hierarchy.py

@@ -1276,8 +1276,6 @@ def group(store=None, overwrite=False, chunk_store=None,
     if zarr_version != 2:
         assert_zarr_v3_api_available()
 
-    if zarr_version == 3 and path is None:
-        raise ValueError(f"path must be provided for a v{zarr_version} group")
     path = normalize_storage_path(path)
 
     if zarr_version == 2:
@@ -1366,10 +1364,6 @@ def open_group(store=None, mode='a', cache_attrs=True, synchronizer=None, path=N
                 "zarr_version of store and chunk_store must match"
             )
 
-    store_version = getattr(store, '_store_version', 2)
-    if store_version == 3 and path is None:
-        raise ValueError("path must be supplied to initialize a zarr v3 group")
-
     path = normalize_storage_path(path)
 
     # ensure store is initialized

zarr/storage.py

@@ -230,8 +230,14 @@ def _getsize(store: BaseStore, path: Path = None) -> int:
         size = 0
         store_version = getattr(store, '_store_version', 2)
         if store_version == 3:
-            members = store.list_prefix(data_root + path)  # type: ignore
-            members += store.list_prefix(meta_root + path)  # type: ignore
+            if path == '':
+                # have to list the root folders without trailing / in this case
+                members = store.list_prefix(data_root.rstrip('/'))   # type: ignore
+                members += store.list_prefix(meta_root.rstrip('/'))  # type: ignore
+            else:
+                members = store.list_prefix(data_root + path)  # type: ignore
+                members += store.list_prefix(meta_root + path)  # type: ignore
+            # also include zarr.json?
             # members += ['zarr.json']
         else:
             members = listdir(store, path)

zarr/tests/test_convenience.py

@@ -73,11 +73,6 @@ def test_open_array(path_type, zarr_version):
     assert isinstance(z, Array)
     assert z.shape == (200,)
 
-    if zarr_version == 3:
-        # cannot open a v3 array without path
-        with pytest.raises(ValueError):
-            open(store, mode='w', shape=200, zarr_version=3)
-
     # open array, read-only
     z = open(store, mode='r', **kwargs)
     assert isinstance(z, Array)
@@ -108,11 +103,6 @@ def test_open_group(path_type, zarr_version):
     assert isinstance(g, Group)
     assert 'foo' not in g
 
-    if zarr_version == 3:
-        # cannot open a v3 group without path
-        with pytest.raises(ValueError):
-            open(store, mode='w', zarr_version=3)
-
     # open group, read-only
     g = open(store, mode='r', **kwargs)
     assert isinstance(g, Group)

zarr/tests/test_core.py

@@ -19,9 +19,6 @@
 
 from zarr._storage.store import (
     v3_api_available,
-    _prefix_to_array_key,
-    _prefix_to_attrs_key,
-    _prefix_to_group_key
 )
 from zarr.core import Array
 from zarr.errors import ArrayNotFoundError, ContainsGroupError
@@ -64,56 +61,64 @@
 class TestArray(unittest.TestCase):
 
     version = 2
+    root = ''
+    KVStoreClass = KVStore
 
     def test_array_init(self):
 
         # normal initialization
-        store = KVStore(dict())
+        store = self.KVStoreClass(dict())
         init_array(store, shape=100, chunks=10, dtype="<f8")
-        a = Array(store)
+        a = Array(store, zarr_version=self.version)
         assert isinstance(a, Array)
         assert (100,) == a.shape
         assert (10,) == a.chunks
         assert '' == a.path
         assert a.name is None
         assert a.basename is None
         assert store is a.store
-        assert "8fecb7a17ea1493d9c1430d04437b4f5b0b34985" == a.hexdigest()
+        if self.version == 2:
+            assert "8fecb7a17ea1493d9c1430d04437b4f5b0b34985" == a.hexdigest()
+        else:
+            assert "968dccbbfc0139f703ead2fd1d503ad6e44db307" == a.hexdigest()
         store.close()
 
         # initialize at path
-        store = KVStore(dict())
+        store = self.KVStoreClass(dict())
         init_array(store, shape=100, chunks=10, path='foo/bar', dtype='<f8')
-        a = Array(store, path='foo/bar')
+        a = Array(store, path='foo/bar', zarr_version=self.version)
         assert isinstance(a, Array)
         assert (100,) == a.shape
         assert (10,) == a.chunks
         assert 'foo/bar' == a.path
         assert '/foo/bar' == a.name
         assert 'bar' == a.basename
         assert store is a.store
-        assert "8fecb7a17ea1493d9c1430d04437b4f5b0b34985" == a.hexdigest()
-
+        if self.version == 2:
+            assert "8fecb7a17ea1493d9c1430d04437b4f5b0b34985" == a.hexdigest()
+        else:
+            assert "968dccbbfc0139f703ead2fd1d503ad6e44db307" == a.hexdigest()
         # store not initialized
-        store = KVStore(dict())
+        store = self.KVStoreClass(dict())
         with pytest.raises(ValueError):
-            Array(store)
+            Array(store, zarr_version=self.version)
 
         # group is in the way
-        store = KVStore(dict())
+        store = self.KVStoreClass(dict())
         init_group(store, path='baz')
         with pytest.raises(ValueError):
-            Array(store, path='baz')
+            Array(store, path='baz', zarr_version=self.version)
 
     def create_array(self, read_only=False, **kwargs):
-        store = KVStore(dict())
+        store = self.KVStoreClass(dict())
         kwargs.setdefault('compressor', Zlib(level=1))
         cache_metadata = kwargs.pop('cache_metadata', True)
         cache_attrs = kwargs.pop('cache_attrs', True)
         write_empty_chunks = kwargs.pop('write_empty_chunks', True)
         init_array(store, **kwargs)
         return Array(store, read_only=read_only, cache_metadata=cache_metadata,
-                     cache_attrs=cache_attrs, write_empty_chunks=write_empty_chunks)
+                     cache_attrs=cache_attrs, write_empty_chunks=write_empty_chunks,
+                     zarr_version=self.version)
 
     def test_store_has_text_keys(self):
         # Initialize array
@@ -162,15 +167,28 @@ def test_nbytes_stored(self):
 
         # dict as store
         z = self.create_array(shape=1000, chunks=100)
-        expect_nbytes_stored = sum(buffer_size(v) for v in z.store.values())
+        if self.version == 3:
+            expect_nbytes_stored = sum(
+                buffer_size(v) for k, v in z.store.items() if k != 'zarr.json'
+            )
+        else:
+            expect_nbytes_stored = sum(buffer_size(v) for v in z.store.values())
         assert expect_nbytes_stored == z.nbytes_stored
         z[:] = 42
-        expect_nbytes_stored = sum(buffer_size(v) for v in z.store.values())
+        if self.version == 3:
+            expect_nbytes_stored = sum(
+                buffer_size(v) for k, v in z.store.items() if k != 'zarr.json'
+            )
+        else:
+            expect_nbytes_stored = sum(buffer_size(v) for v in z.store.values())
         assert expect_nbytes_stored == z.nbytes_stored
 
         # mess with store
         try:
-            z.store[z._key_prefix + 'foo'] = list(range(10))
+            if self.version == 2:
+                z.store[z._key_prefix + 'foo'] = list(range(10))
+            else:
+                z.store['meta/root/foo'] = list(range(10))
             assert -1 == z.nbytes_stored
         except TypeError:
             pass
@@ -1003,7 +1021,7 @@ def test_nchunks_initialized(self):
 
             assert 0 == z.nchunks_initialized
             # manually put something into the store to confuse matters
-            z.store['foo'] = b'bar'
+            z.store[self.root + 'foo'] = b'bar'
             assert 0 == z.nchunks_initialized
             z[:] = 42
             assert 10 == z.nchunks_initialized
@@ -2703,36 +2721,25 @@ def test_read_from_all_blocks(self):
 # StoreV3 test classes inheriting from the above below this point
 ####
 
-# Start with TestArrayWithPathV3 not TestArrayV3 since path must be supplied
-
 @pytest.mark.skipif(not v3_api_available, reason="V3 is disabled")
-class TestArrayV3(unittest.TestCase):
+class TestArrayV3(TestArray):
 
     version = 3
+    root = meta_root
+    KVStoreClass = KVStoreV3
 
-    def test_array_init(self):
-
-        # normal initialization
-        store = KVStoreV3(dict())
-        with pytest.raises(ValueError):
-            # cannot init_array for v3 without a path
-            init_array(store, shape=100, chunks=10, dtype="<f8")
-
-        init_array(store, path='x', shape=100, chunks=10, dtype="<f8")
-        with pytest.raises(ValueError):
-            # cannot initialize a v3 array without a path
-            Array(store)
-
-    def test_prefix_exceptions(self):
-        store = KVStoreV3(dict())
-        with pytest.raises(ValueError):
-            _prefix_to_array_key(store, '')
-
-        with pytest.raises(ValueError):
-            _prefix_to_group_key(store, '')
+    def expected(self):
+        # tests for array without path will not be run for v3 stores
+        assert self.version == 3
+        return [
+            "73ab8ace56719a5c9308c3754f5e2d57bc73dc20",
+            "5fb3d02b8f01244721582929b3cad578aec5cea5",
+            "26b098bedb640846e18dc2fbc1c27684bb02b532",
+            "799a458c287d431d747bec0728987ca4fe764549",
+            "c780221df84eb91cb62f633f12d3f1eaa9cee6bd"
+        ]
 
-        with pytest.raises(ValueError):
-            _prefix_to_attrs_key(store, '')
+    # TODO: fix test_nbytes_stored
 
 
 @pytest.mark.skipif(not v3_api_available, reason="V3 is disabled")
@@ -2754,10 +2761,19 @@ def create_array(array_path='arr1', read_only=False, **kwargs):
 
     def test_array_init(self):
 
-        # should not be able to initialize without a path in V3
         store = KVStoreV3(dict())
-        with pytest.raises(ValueError):
-            init_array(store, shape=100, chunks=10, dtype="<f8")
+        # can initialize an array without a path
+        init_array(store, shape=100, chunks=10, dtype="<f8")
+        b = Array(store)
+        assert not b.is_view
+        assert isinstance(b, Array)
+        assert (100,) == b.shape
+        assert (10,) == b.chunks
+        assert '' == b.path
+        assert b.name is None
+        assert b.basename is None
+        assert store is b.store
+        assert "968dccbbfc0139f703ead2fd1d503ad6e44db307" == b.hexdigest()
 
         # initialize at path
         store = KVStoreV3(dict())
@@ -2797,11 +2813,6 @@ def test_array_init(self):
         assert group_key not in store
         assert (meta_root + path + '.array.json') in store
 
-    def test_array_no_path(self):
-        # passing path=None to init_array will raise an exception
-        with pytest.raises(ValueError):
-            self.create_array(shape=1000, chunks=100, array_path=None)
-
     def expected(self):
         return [
             "73ab8ace56719a5c9308c3754f5e2d57bc73dc20",